In the drilling of oil wells, gas wells, and the like, it is conventional practice to use a drilling mud to enhance the efficiency of the operation. The drilling mud is continuously circulated from a storage area on the surface, downward through the drill pipe, and then upward through the borehole to the surface. The purpose of the mud is to remove drilled solids, such as cuttings and formation cavings, from the borehole to the surface. It also serves to cool and lubricate the bit, to form a filter cake on the borehole wall, and to prevent pressure from being lost if a void or high pressure gas pocket is encountered.
Drilling muds usually contain a number of components, including barium, hematite, iron sulfite, and the like. They are kept in containers near the drilling rig, each of the containers holding different grades of drilling mud for use at different levels of the drill. Before use in many applications, the above components may be mixed with oil to produce the final form of mud.
In order for drilling mud to perform its desired functions, it is necessary to maintain its viscosity and density within prescribed limits. This is difficult when it is considered that drill cuttings and formation cavings are constantly and inherently being accumulated in the mud, thereby increasing its viscosity and density. Therefore, in customary operations the practice is to separate solids from the mud which is returned to the surface. A technique commonly employed is to pass the mud first through a vibrating screen, sometimes referred to as a shale shaker, to remove the large cuttings and other particles, and then through a series of hydrocyclones to remove smaller size particles. The mud which passes through both the vibrating screen and the hydrocyclones is returned to the storage bins for reuse, and the solids removed from the mud are discarded at various places surrounding the drill site.
The discarded solids present a significant disposal and environmental problem. After the well is shut down, the site must be cleaned. The contents of the slush ponds containing the discarded materials must be dug up and hauled away to toxic waste dumps. The expense of this, plus the cost and effort involved in obtaining the necessary toxic waste permits, plus the continuing liability from potential damage from the waste, creates a serious problem.
It is an object of the present invention to provide methods for cleansing discarded materials from the drilling mud operations, without any materials being hauled to toxic disposal sites.
It is a further object of the invention to carry out the cleansing operation in such manner that drill cuttings and formation cavings may be cleansed and returned to the soil surrounding the drill site free of contamination.
It is another object to separate desired drilling mud components from the discarded material and make them available for re-use in further drilling mud formulae.
It is still another object to accomplish the cleansing operation with reagents which may be restored and recycled through the cleaning system to substantially reduce the cost of operation.
It is yet another object to provide apparatus and equipment for accomplishing the foregoing.
Other objects and advantages will become apparent as the specification proceeds.